Inferior Rectal Nerve

The Inferior Rectal nerve, a branch of the pudendal nerve, is sensory to the anal canal and surrounding skin. It innervates the sphincter ani externus muscle.

External hemorrhoids are masses of dilated tortuous veins that occur below the pectinate line. They are painful due to the somatic sensory distribution of the inferior rectal nerve. The visceral sensory distribution above the pectinate line lacks pain fibers; therefore, internal hemorrhoids are devoid of pain.